1841 is between 2 network at left 10.0.XX 255.255.0.0 and at right 10.254.0.X 255.255.255.0 routage table is ok but a computer at left with 10.0.0.76 not ping a computer a right 10.254.0.2 !!!!!!!!!
not firewall so what is the probleme please ?
In a situation such as you describe the first thing I would check would be to verify that the router is able to ping both PCs. This will verify local connectivity and reachability. It will also check on the possibility that the PCs may be running a firewall which is denying ping.
If the router can ping both PCs then the next thing that I would check as a possible problem is what do the PCs have configured as their default gateway (also check to verify that the IP address and mask configured are correct). Many times this kind of problem is a mis-configured default gateway.